Not only a hard disk drive (HDD) but also a solid state drive (SDD) has been used as an external storage device for an information processing device, such as a personal computer. The SDD includes a NAND flash memory as a nonvolatile semiconductor memory.
For example, when the SDD is used in the same environment as the HDD, if data is rewritten frequently, the SDD will age (wear out) faster. Therefore, if test (screening) before product shipment is insufficient, the failure rate after shipment will increase.
One method of increasing the reliability of the SSD is to rewrite data in the SSD repeatedly in the screening process. However, when such screening is performed, screening time and screening costs will increase.